Bioinformatics analysis
The function annotation and classification of the identified DEPs were performed based on Gene Ontology (http://www.geneontology.org/) and Uniprot (http://www.uniprot.org/) databases.25,26Subcellular location prediction analysis was conducted with WoLF PSORT tool (http://wolfpsort.org/).27The hierarchical clustering analysis of the protein expression profiles under different Ca levels was performed referring Hu et al.28 Fold changes of protein abundances were calculated by dividing the density value of DEPs at low Ca level or high Ca level by that at media Ca level. The resulted values were log2 transformed and inputted into the Cluster software (version 3.0) with complete linkage algorithm setting. The hierarchical cluster results were visualized with TreeView software version 1.1.3. For PPI network construction, the STRING database and Cytoscape software was used.29